Safety Compliance for Mobile Drive Units

ABSTRACT

Techniques for making a physical area safe for a human to enter when mobile drive units (e.g., robots) are operating in the physical area are described. A management device may send an activity message to the mobile drive units instructing the mobile drive units to perform a set of activities. If a human is detected in the physical area, the management device may stop sending the activity command. If the mobile drive units do not receive the activity command, the mobile drive units may stop performing the set of activities. After the management device determines that the human has left the physical area, the management device may resume sending the activity message.

BACKGROUND

An industrial robot is an electro-mechanical machine that is controlledby a computer program, electronic circuits, or both. The industrialrobot may be either stationary or mobile (e.g., capable of navigatingfrom one location to another location). For example, the industrialrobot may have wheels (or another form of conveyance) to enable theindustrial robot to navigate to different locations. Industrial robotsthat can navigate independently of each other may be referred to asmobile drive units (MDUs). The MDUs may be capable of performingactivities using one or more arm-like mechanisms to grasp an item,release the item, etc. Based on the type of task that is to beperformed, two or more MDUs may coordinate their respective activitiesto perform a task.

In an area (e.g., a factory, a warehouse, a materials handling facilityor similar type of setting) where multiple MDUs are performingactivities, under some circumstances, humans may enter the area. Forexample, plastic wrap used to cover a load of items may foul the wheelsof an MDU. As another example, an item from the load of items may falland obstruct the path of an MDU or partially damage an MDU. Under suchcircumstances, a human may enter the area to perform an activity such asremoving the plastic wrap from the wheels of the MDU, removing an itemobstructing the path of the MDU, or repairing the MDU. The MDUs may beinstructed to perform one or more activities, such as transporting itemsbetween locations in a materials handling facility, transporting ashelving unit from one location to another, docking with a chargingunit, handing off a trash container to a dumper unit, etc. When a humanenters an area in which multiple MDUs have been instructed to performone or more activities, the human may risk being inadvertently injuredby one or more of the MDUs as the MDUs perform their activities.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description is described with reference to the accompanyingfigures. In the figures, the left-most digit(s) of a reference numberidentifies the figure in which the reference number first appears. Thesame reference numbers in different figures indicate similar oridentical items.

FIG. 1 is an illustrative architecture that includes instructing mobiledrive units within a first distance from a human to stop performingphysical activities according to some implementations.

FIG. 2 is an illustrative architecture that includes a moveable zoneaccording to some implementations.

FIG. 3 is an illustrative architecture that includes a fixed zoneaccording to some implementations.

FIG. 4 is an illustrative architecture that includes multipleconfigurable zones according to some implementations.

FIG. 5 is an illustrative architecture in which an activity message isdelivered to mobile drive units at a predetermined interval according tosome implementations.

FIG. 6 is an illustrative architecture that includes using identifiersto determine location information according to some implementations.

FIG. 7 is an illustrative architecture in which a mobile drive unitdetects the presence of a human according to some implementations.

FIG. 8 is a flow diagram of an example process that includes sending anactivity message according to some implementations.

FIG. 9 is a flow diagram of an example process that includes instructingmobile drive units to avoid a portion of an area according to someimplementations.

DETAILED DESCRIPTION

The systems and techniques described herein may be used to provide afunctionally safe environment for humans in an area in which mobiledrive units (MDUs) are performing activities. For example, when a humanis detected within an area in which MDUs are performing activities, asafety management device may instruct at least some of the MDUs totemporarily cease performing activities. As used herein, the termactivity refers to physical activity, e.g., physical movement. Thus,during the time that the MDUs cease performing activities, the MDUs maycontinue to receive signals, transmit signals, perform computations, andperform other non-physical activities.

The human may wear a locator device that the safety management device oran MDU uses to determine a location of the human. When the safetymanagement device or one of the MDUs determines that the human islocated in or near an area in which MDUs are performing activities, MDUswithin a first distance from the human may be instructed to temporarilycease performing a set of activities. In some cases, MDUs within asecond distance from the human may be instructed to reduce their speed.Additionally, some of the MDUs may be instructed to navigate to a newlocation and then temporarily stop performing any activity. Thus, whenthe presence of a human is detected, a first set of MDUs may temporarilystop performing any activity, a second set of MDUs may reduce theirspeed of travel, and/or a third set of MDUs may retreat (e.g., navigateto a new location that is further away from the human) and thentemporarily stop performing any activity.

An MDU may be a robotic (e.g., electro-mechanical) device that can beinstructed to perform a set of activities and may be capable ofnavigating to different locations using a drive mechanism, such aswheels or other conveyance mechanism. The MDUs may be instructed toperform a set of activities. For example, each MDU may be instructed toreceive a listing of items to be shipped to a particular address,retrieve the items from the listing from multiple locations (e.g.,multiple bins of items), place the retrieved items in a container forshipment to the particular address, perform another type of task, or anycombination thereof.

The location of the human may be determined using a variety oftechniques. For example, the human may wear a locator device thattransmits a signal, such as a radio frequency identifier (RFID). Asanother example, the human may wear a locator device that determines aposition of the device (e.g., using a triangulation method, globalpositioning satellites (GPS), or the like) and sends the locationinformation to the MDUs and/or to a management device that controls theMDUs. As a further example, the human may wear a device that transmits(e.g., broadcasts) a signal that may be triangulated using antennasplaced at various locations within the area in which the MDUs areperforming activities. As yet another example, the human may wear adevice that reads (e.g., using optical recognition, RFID, etc.)identifiers, such as fiducial markers, that have been distributedthroughout the area and sends data associated with the identifiers toenable the location of the human to be determined. As yet anotherexample, imaging devices, such as cameras, placed at various locationsin an area may be used to optically or visually determine a location ofthe human. As a further example, sensors (e.g., floor sensors, heatsensors, motion sensors, etc.) may be placed at various locations in anarea to determine a location of the human. Of course, any combination ofthe previously mentioned techniques, potentially in combination withother location determination techniques, may be used to determine thelocation of the human.

The safety management device may track the locations of humans and thelocations of MDUs. The safety management device may use varioustechniques to create a functionally safe environment for humans. Forexample, the safety management device may create one or more fixed(e.g., immovable) zones and track the location of humans entering andleaving the fixed zones. In some cases, the safety management device maynot track the location of the humans within the fixed zones while inother cases the safety management device may track the location of thehumans within the fixed zones. In some implementations, the safetymanagement device may create a moveable zone around a human. Forexample, the safety management device may continually monitor a locationof each human in an area, each MDU in the area, determine a distance ofeach MDU from each human, and then instruct the MDUs to perform acommand (e.g., stop performing physical activities, reduce speed, moveto a new location, etc.) based on each MDU's distance from the human. Toillustrate, the human may wear a locator device that includes a readerdevice to scan identifiers, such as fiducial markers, placed at variouslocations within an area. To illustrate, the identifiers may be placedon the floor or at a certain height to enable the reader toautomatically scan the identifiers and transmit the read information tothe safety management device. In some cases, the information read fromthe identifiers may include location information associated with acorresponding location of each of the identifiers.

As another example, the humans may wear a locator device that includes aradio frequency identifier (RFID) reader to read RFID tags placed atvarious locations (e.g., on the floor, at a particular height, infiducial markers, etc.) within an area. As yet another example,individual MDUs may detect the presence of a human by receiving a signaltransmitted (e.g., broadcast) by a locator device that is worn by thehuman. To illustrate, each human may wear a locator device thattransmits or broadcasts a signal, such as an RFID signal or other typeof signal. In this example, the MDUs may detect the presence of humansby detecting the signal (e.g., RFID or similar signal) that is beingtransmitted or broadcast by the locator device worn by each human. As afurther example, an indoor positioning system may be used to track thelocation of each human that enters an area in which one or more MDUs areperforming activities. To illustrate, antennas placed at variouslocations in the area may be used to determine (e.g., usingtriangulation) a location of each locator device worn by each human. Thelocator device may transmit or broadcast using one or more frequenciesto enable the location to be determined relatively quickly.

When a safety management device detects that a human has entered an areain which MDUs are performing activities, the safety management devicemay create a safe zone by instructing MDUs within a predetermineddistance from the human to stop performing any physical activities. Thesafety management device may instruct MDUs that are more than thepredetermined distance from the human to avoid entering the safe zone.As the human moves within the area, the safety management device maytrack the location of the human and the locations of the MDUs. Based onthe distance of the MDUs from the human, the safety management devicemay instruct at least some of the MDUs to either (i) stop performing anyphysical activity and/or (ii) avoid a portion of the area (e.g., thesafe zone).

When the safety management device instructs an MDU to cease performingphysical activities, in some cases the instruction may cause theconnection of a portion of the MDU to a power source to be interrupted.For example, the instruction to cease performing physical activities maycause the connection that provides power to the wheels (or other meansof conveyance for the MDU) to be temporarily interrupted. As anotherexample, the instruction to cease performing physical activities maycause the connection that provides power to the various electroniccomponents of the MDU to be temporarily interrupted.

Thus, when the presence of a human is detected in or near (e.g., withina predetermined distance from) an area in which MDUs are performingactivities, the MDUs may temporarily stop performing the activities. Insome cases, the MDUs may perform another activity, such as navigating toa new location. For example, the MDUs may move to a location that isgreater than a predetermined distance from the estimated path of thehuman and then temporarily stop performing any activity. The presence ofthe human may be detected by one or more MDUs and then transmitted orbroadcast to other MDUs in the area and/or a management device. Thepresence of the human may be detected by a management device andtransmitted or broadcast to at least one of the MDUs in the area. Thepresence of the human may be detected using one or more techniques, suchas (1) sensors interspersed throughout the area, (2) imaging devicescapable of capturing images of the area, (3) a device worn by the humanthat receives and/or sends location information, and/or (4) other meansof detection.

Mobile Drive Units Instructed Based on a Distance from a Human

FIG. 1 is an illustrative architecture 100 that includes instructingmobile drive units within a first distance from a human to stopperforming physical activities according to some implementations. Thearchitecture 100 includes an area 102 with one or more fixed objects104, such as the representative fixed objects 104(1), 104(2), 104(3) and104(4). The fixed objects may include, for example, items, a load ofitems, shelves to store items, pillars, machinery, tables, other objectsthat are not moved very often, or any combination thereof. Thearchitecture 100 illustrates how the area 102 may be made functionallysafe for humans.

The area 102 may include one or more mobile drive units (MDU) 106, suchas the representative MDUs 106(1), 106(2), 106(3) and 106(4). One ormore of the MDUs 106 may be airborne, e.g., capable of travellingthrough three dimensional space. Individual mobile drive units of theMDUs 106 may be instructed to perform a set of activities, such asplacing items onto one or more of the fixed objects 104, selecting andremoving one or more items from the fixed objects 104, moving betweenthe fixed objects 104 to perform the set of activities, moving itemsfrom one of the fixed objects 104 to another of the fixed objects 104,etc.

An operational management device 108 may be used to control theoperations or activities of the MDUs 106. For example, the operationalmanagement device 108 may instruct individual mobile drive units of theMDUs 106 to perform a particular set of activities. For example, theoperational management device 108 may wirelessly transmit a firstcommand (e.g., to perform a first set of activities) to the MDU 106(1),wirelessly transmit a second command (e.g., to perform a second set ofactivities) to the MDU 106(2), and so on.

A safety management device 110 may control the MDUs 106 to provide afunctionally safe environment for humans in the area 102. For example,each of the MDUs 106 may periodically, at an interval of N milliseconds(where N>0), send a query message asking if each MDU can perform (orcontinue performing) the set of activities that the operationalmanagement device 108 has instructed the MDUs 106 to perform. Each querymessage may include (i) a unique identifier and (ii) an identity of thesending mobile drive unit. For example, a query message sent by MDU106(1) may indicate that the query message was sent by MDU 106(1). Insome cases, the query message may include a time stamp. For example, theunique identifier may include a time stamp that includes a date and timethat the query message was sent along with an identity of the sendingmobile drive unit. The safety management device 110 may respond to eachquery message that the safety management device 110 receives from theMDUs 106. For example, a response message to a query message mayinstruct a particular one of the MDUs 106 to (i) continue performing aset of activities, (ii) temporarily stop performing the set ofactivities, (iii) reduce a speed of the particular MDU when moving fromone location to another location, (iv) move to a new location, (v) moveto a new location and temporarily not perform any physical activities,and so on. Thus, a particular mobile drive unit of the MDUs 106 mayperform (or continue performing) the set of activities when theparticular mobile drive unit has a received a response to a mostrecently sent query message instructing the particular mobile drive unitto continue performing the set of activities. A particular mobile driveunit of the MDUs 106 may stop performing the set of activities when theparticular mobile drive unit fails to receive a response to a mostrecently sent query message or when the particular mobile drive unitreceives an instruction to stop performing any physical activity. Insome cases, a particular mobile drive unit of the MDUs 106 may stopperforming the set of activities when the particular mobile drive unitfails to receive more than M response messages (where M>0).

In some implementations, each of the MDUs 106 may periodically, at aninterval of N milliseconds (where N>0), receive a message from thesafety management device 110 without the MDUs 106 periodically sendingquery messages to the safety management device 110. For example, thesafety management device 110 may periodically send an instructionalmessage to each of the MDUs 106, instructing each of the MDUs 106 to (i)continue performing a set of activities, (ii) temporarily stopperforming the set of activities, (iii) reduce a speed of the particularMDU when moving from one location to another location, (iv) move to anew location, or (v) move to a new location and temporarily not performany physical activities. Thus, in such implementations, the safetymanagement device 110 may send instructional messages rather thanresponses to query messages sent by the MDUs 106.

Various types of techniques may be used to track the location of each ofthe MDUs 106 and the location of humans, such as the human 118. One ormore imaging devices 112 (e.g. cameras), such as representative imagingdevices 112(1), 112(2), 112(3) and 112(4), may be placed at variouslocations in the area 102 to provide information used to track mobiledrive units and humans. The cameras 112 may provide image data to enablethe operational and safety management devices 108, 110 to track themovement and determine a location of each of the MDUs 106 and the humansin the area 102. One or more sensors 114, such as representative sensors114(1), 114(2), 114(3) and 114(4), may be placed at various locations inthe area 102 to provide sensor data to track the movement and determinea location of each of the MDUs 106 and the humans in the area 102. Thesensors 114 may include motion sensors, heat sensors, infrared sensors,pressure sensors, another type of sensor, or any combination thereof.

Identifiers 116 (e.g., fiducial markers), such as representativeidentifiers 116(1), 116(2), 116(3) and 116(4), may be placed at variouslocations in the area 102. The identifiers 116 may be read by (i) alocator device worn by a human, such as a representative human 118, or(ii) a locator device mounted on each of the MDUs 106. In FIG. 1, alocator device 120 is illustrated as being worn by the human 118. Thelocator device 120 may include a reader device that is capable ofreading the identifiers 116. For example, the identifiers 116 mayinclude an optically scannable code, such as a bar code or quickreference (QR) code, that can be scanned by a code reader device. Asanother example, the identifiers 116 may broadcast an RFID signal thatcan be read by an RFID reader device. A locator device, such as thelocator device 120, may scan, read, or receive signals from a particularidentifier of the identifiers 116 when the locator device 102 is withina predetermined distance from the particular identifier and transmit atleast a portion of the data scanned, read, or received from theparticular identifier to at least one of the management devices 108,110. Each of the identifiers 116 may provide data that enables themanagement devices 108, 110 to determine a location of the human 118and/or a location of the MDUs 106. For example, each of the identifiers116 may have a unique identifier and the management devices 108, 110 maybe capable of mapping the unique identifier to a specific location inthe area 102. In some cases, the data provided by scanning, reading, orreceiving signals from one of the identifiers 116 may include a locationof the identifier that is being scanned. For example, when the locatordevice 120 scans, reads, or receives signals from the identifier 116(2),the locator device 120 may receive data that includes a location of theidentifier 116(2). The locator device 120 may send the data from theidentifier 116(2) to the management devices 108, 110 to enable themanagement devices 108, 110 to determine that the human 118 is locatednear the location of the identifier 116(2).

The safety management device 110 may determine a location of each of theMDUs 106. In some cases, when a human is determined to be present in ornear the area 102, the safety management device 110 may instruct all theMDUs 106 to temporarily stop performing any physical activities. If oneor more of the MDUs 106 are airborne, the airborne MDUs may beinstructed to land in a controlled manner and then stop performing anyphysical activities. In other cases, when humans are present in or nearthe area 102, the safety management device 110 may determine a locationof each of the humans, such as a location of the human 118. When thesafety management device 110 determines that a human is in (or near) thearea 102, the safety management device 110 may determine a location ofeach of the MDUs 106 and instruct the MDUs 106 to perform a command,e.g., based on the distance of a particular MDU from the human 118. Thecommands to the MDUs 106 may include stop performing physicalactivities, change from a faster speed to a slower speed when movingfrom one location to another location, move to a new location, etc. Forexample, the safety management device 110 may determine that an MDU,such as the MDU 106(1), is within a first distance 122 from the human118 and instruct the MDU to stop performing physical activities (e.g.,to ensure the safety of the human 118). As another example, the safetymanagement device 110 may determine that an MDU, such as the MDU 106(2),is within a second distance 124 (e.g., greater than the first distance122) from the human 118 and instruct the MDU to change from a fasterspeed to a slower speed when moving from one location to anotherlocation. In this example, the safety management device 110 maydetermine that the MDU 106(2) is within the second distance 124 from thehuman 118, but will not travel within the first distance 122 from thehuman 118, and may thus instruct the MDU 106(2) to reduce speed, ratherthan stop all physical activities. Alternatively or additionally, thesafety management device 110 may instruct the MDU 106(2) within thesecond distance 124 from the human 118 to navigate away from thelocation of the human 118 until the MDU 106(2) is outside the seconddistance 124 from the human, for example, and then continue performing aset of activities while maintaining at least the second distance 124from the human, or stop all physical activities. The safety managementdevice 110 may instruct MDUs within a remaining portion 126, e.g.,outside the second distance 124 from the human 118, of the area 102,such as the MDU 106(3) and MDU 106(4), to each continue performing a setof activities. Alternatively or additionally, the safety managementdevice 110 may instruct the MDUs 106(3) and 106(4) to navigate furtheraway from the location of the human 118 and then continue performing aset of activities while maintaining a further specified distance fromthe human, or stop all physical activities. If one or more of the MDUs106 are airborne, the airborne MDUs 106 may be instructed to land in acontrolled manner. For example, the airborne MDUs 106 may be instructedto land in such a way that after landing, the previously airborne MDUs106 are at least the first distance 122 from the human 118. Toillustrate, the airborne MDUs 106 may be instructed to land in acontrolled manner in a portion of the area 102 that is greater than thefirst distance 122 but may be less than the second distance 124. Afterlanding, the previously airborne MDUs 106 may be instructed to stopperforming all physical activities. In some cases, if the airborne MDUs106 are within the first distance 122 from the human 118, the airborneMDUs 106 may be instructed to drop to the ground (e.g., by cutting powerto the mechanism that is keeping the MDUs 106 airborne) or land in acontrolled manner. Airborne MDUs 106 that are the second distance 124(or greater) from the human 118 may be instructed to land in acontrolled manner, navigate to a new location that is a greater that thesecond distance 124 from the human 118, stop performing any physicalactivities, or any combination thereof.

The safety management device 110 may effectively create a moveable zone128 by tracking the movement of the human 118 in the area 102 inreal-time and instructing the MDUs 106 accordingly. For example, if thehuman 118 moves towards the MDU 106(2), the safety management device 110may determine that the MDU 106(2) is within the first distance 122 fromthe human 118 and instruct the MDU 106(2) to stop performing anyphysical activities. The safety management device 110 may determine thatthe MDU 106(3) is within the second distance 124 from the human 118 andinstruct the MDU 106(3) to reduce speed. The safety management device110 may continue tracking the movement of the human 118 in real-time andinstructing the MDUs 106 accordingly until the safety management device110 determines that the human 118 is no longer in the area 102.

For illustration purposes, the moveable zone 128 is shown as beingcircular in FIG. 1. However, it should be understood that the moveablezone 128 may take the form of any geometric shape (e.g., square,rectangle, triangle, or the like) or any non-geometric shape. Inaddition, while the first distance 122 and the second distance 124 areillustrated in FIG. 1, the number of distances and the instructionsprovided to the MDUs based on the distance may vary. For example, insome implementations, MDUs within the first distance 122 may beinstructed to stop performing any physical activity while MDUs that aregreater than the first distance 122 from the human 118 may be instructedto continue performing a set of activities.

The safety management device 110 may include a redundant architecturesuch that the safety management device 110 can continue to function byinstructing the MDUs 106 even after the failure of a hardware componentor a software component. For example, when a hardware component fails,the safety management device 110 may detect the failure and switch tousing a backup hardware component.

In some implementations, the function of the management devices 108, 110may be distributed among the MDUs 106. For example, a mobile drive unit(e.g., MDU 106(1)) that is closest to the human 118 may detect thepresence of the human 118, and send instructions to the other MDUs 106(e.g., MDU 106(2), MDU 106(3), and MDU 106(4)) to perform variousactions, such as reducing speed or navigating to a new location.

When the safety management device 110 or one (or more) of the MDUs 106determines that the human 118 has exited (e.g., is no longer present in)the area 102, individual drive units of the MDUs 106 may resumeperforming a set of activities. In some cases, at least some of the MDUs106 may resume the activities that were being performed before thepresence of the human 118 was detected in the area 102. In other cases,at least some of the MDUs 106 may perform a different set of activitiesas compared to the set of activities that were being performed beforethe presence of the human 118 was detected in the area 102.

Thus, when the presence of a human is detected in an area, a safetymanagement device may continually monitor in real-time a location of thehuman, a location of individual mobile drive units, and/or a distance ofthe mobile drive units from the human. In some implementations, based onthe distance of the individual mobile drive units from the human, thesafety management device may continually send updated instructions tothe mobile drive units.

Creating a Moveable Zone

FIG. 2 is an illustrative architecture 200 that includes a moveable zoneaccording to some implementations. Initially, before a human isdetected, the MDUs 106 may perform activities as directed by theoperational management device 108, and as confirmed by the safetymanagement device 110, free of any special restrictions or safetyconsiderations, as shown in the upper panel of FIG. 2. Suppose, however,that the human 118 enters the area 102, as shown in the lower panel ofFIG. 2. When the presence of the human 118 is detected, e.g., vialocator device 120, at a first location 202 in the area 102, the safetymanagement device 110 may create the moveable zone 128 around the human118 to create a functionally safe environment. For example, based on adistance of each of the MDUs 106 from the human 118, the safetymanagement device 110 may instruct individual mobile drive units of theMDUs 106 to (i) continue performing a set of activities, (ii)temporarily stop performing the set of activities, (iii) reduce speedwhen moving from one location to another location, (iv) move to a newlocation, or (v) move to a new location and temporarily stop performingphysical activities. To illustrate, some of the MDUs 106 that are withina first distance from the human 118 may be instructed to perform a firstcommand (e.g., temporarily stop performing any physical activities),while others of the MDUs 106 that are at greater than the first distancebut within a second distance from the human 118 may be instructed toperform a second command (e.g., temporarily reduce speed when movingfrom one location to another location).

The safety management device 110 may continually monitor the location ofthe human 118 within the area 102, continually monitor the location ofeach of the MDUs 106 within the area 102, and instruct individual onesof the MDUs 106 to perform a command based on the distance of the MDUs106 from the human 118. For example, when the human 118 moves from thefirst location 202 to a second location 204 in the area 102, the safetymanagement device 110 may determine that the MDU 106(3) is within thefirst distance 122 from the human 118 at the second location 204 andinstruct the MDU 106(3) to temporarily stop performing any physicalactivities.

In some cases, at least one of the MDUs 106 may detect the presence ofthe human 118 in the area 102 and alert the safety management device110, the other MDUs 106, or both as to the presence of the human 118.When a particular MDU of the MDUs 106 detects the presence of the human118, the particular MDU may determine a distance between the particularMDU and the human 118 and automatically perform an action, such astemporarily stopping all physical activities.

When the management device 108 and/or at least one (or all) of the MDUs106 determines that the human 118 is no longer present in the area 102,individual drive units of the MDUs 106 may resume performing a set ofactivities. In some cases, at least some of the MDUs 106 may resume theactivities that were being performed before the presence of the human118 was detected in the area 102. In other cases, at least some of theMDUs 106 may perform a different set of activities as compared to theset of activities that were being performed before the presence of thehuman 118 was detected in the area 102.

The presence or absence of the human 118 in the area 102 may bedetermined using the locator device 120, the imaging devices 112, thesensors 114, the identifiers 116, the MDUs 106, using another technique,or any combination thereof.

Thus, when the presence of a human is detected in an area in which MDUsare performing a set of activities, the MDUs may temporarily stopperforming the set of activities. When a determination is made that thehuman is no longer present in the area, the MDUs may resume performingthe set of activities. In this way, the MDUs may provide a functionallysafe environment to prevent the human from being inadvertently injuredby the MDUs.

Creating a Fixed Zone

FIG. 3 is an illustrative architecture 300 that includes a fixed zoneaccording to some implementations. In some situations, the human 118 mayperform activities in a portion of the area 102 but not outside theportion. For example, the human 118 may perform repairs to a piece ofequipment in the area 102, perform repairs to one of the MDUs 106, addor adjust shelves to one of the fixed objects 104, etc. In suchsituations, the human 118 may use a relatively fixed portion of the area102, e.g., a work area.

To create such an area, the human 118 may instruct the safety managementdevice 110 to create a fixed zone 302. For example, the human 118 mayspecify a location and a size of the fixed zone 302. The fixed zone 302may be created using barriers 304. The barriers 304 may include virtualbarriers, physical barriers, or both.

To create the fixed zone 302 using virtual barriers 304, the safetymanagement device 110 may instruct the MDUs 106 to avoid entering aportion of the area 102 that includes the fixed zone 302. In some cases,the safety management device 110 may instruct one or more of the MDUs106 to place transmitters (e.g., light curtains or similar devices)along a perimeter of the fixed zone 302. Alternatively, the human 118may place transmitters along a perimeter of the fixed zone 302. Thetransmitters may broadcast a signal that causes the MDUs 106 to avoidentering a portion of the area 102 that includes the fixed zone 302.

To create the fixed zone 302 using physical barriers, the safetymanagement device 110 may instruct the MDUs 106 to place the (physical)barriers 304 to mark the boundary of the safe zone 302. Alternatively,the human 118 may place transmitters along a perimeter of the fixed zone302. The MDUs 106 may each include one or more sensors that are capableof identifying the (physical) barriers 304. For example, the MDUs 106may sense the (physical) barriers 304 as walls (or other fixed objects)that are to be avoided when navigating the area 102. In someimplementations, the physical barriers 304 may include transmitters thattransmit a signal that instructs the MDUs 106 to avoid a portion of thearea 102 that includes the fixed zone 302. In such an implementation,the barriers 304 may include both physical barriers and virtualbarriers. If the virtual barrier fails (e.g., a particular MDU attemptsto enter the fixed zone 302 because a transmitter failed or because theparticular MDU's sensor failed), the physical barrier may prevent theparticular MDU from entering the fixed zone 302.

During the time that the fixed zone 302 is created, the MDUs 106 mayavoid coming within a specified (e.g., predetermined) distance of thefixed zone 302. When the safety management device 110 determines thatthe human 118 is no longer present in the area 102, the safetymanagement device 110 may instruct the MDUs 106 to resume performing aset of activities, including activities that involve entering theportion of the area 102 that was used to create the fixed zone 302. Ifphysical barriers were used to create the fixed zone 302, after thehuman has left the area 102, the safety management device 110 mayinstruct the MDUs 106 to remove the physical barriers. Alternatively,the human 118 may remove the physical barriers from the fixed zone 302.

In some cases, as a further safety measure, individual ones of the MDUs106 that come within a predetermined distance of the fixed zone 302 (orthe barriers 304) may perform an action, e.g., similar to the moveablezone 128 of FIG. 1. For example, individual ones of the MDUs 106 thatcome within a first predetermined distance from the fixed zone 302 (orthe barriers 304) may stop performing physical activities whileindividual ones of the MDUs 106 that are within a second predetermineddistance may reduce speed.

Thus, a fixed zone that is functionally safe may be created to enable ahuman to perform actions without risking injury by an MDU. The fixedzone may be created using physical barriers, virtual barriers, or acombination of both.

Configurable Zones

FIG. 4 is an illustrative architecture 400 that includes multipleconfigurable zones according to some implementations. As discussed abovewith respect to FIGS. 1, 2, and 3, various types of zones, includingmoveable zones and fixed zones, may be created when the human 118 ispresent in the area 102.

The architecture 400 illustrates how an area, such as the area 102, mayinclude multiple zones in which each zone can be configured orreconfigured as desired to be one of the zones described in FIG. 1, 2,or 3. In FIG. 4, the area 102 includes a first zone 402 and a secondzone 404. Of course, depending on the implementation, an area may havemore or fewer than two zones.

Each of the zones 402 and 404 may be configurable and the behavior ofthe MDUs 106 that are present may depend on various factors, including asetting of the locator device 120, a current time and/or date, otherfactors, or any combination thereof. For example, when the presence ofthe human 118 is detected in the first zone 402, the MDUs 106 may slowdown or stop performing physical activities (e.g., as illustrated inFIGS. 1 and 2). As another example, the second zone 404 may be a fixedzone (e.g., as illustrated in FIG. 3) during a particular time period ona particular day of the week. For example, the second zone 404 may be asafe zone every Friday between 2:00 and 4:00 PM, to enable maintenanceto be performed. During other times, the second zone 404 may be amoveable zone that surrounds a second human 406 when the second human406 is detected in the area 102. The second human 406 may wear a secondlocator device 408 to enable the safety management device 110 to trackthe location of the second human 406.

In some cases, the locator devices 120, 408 may include settings thatspecify the behavior of the MDUs 106. For example, a first setting maycause MDUs 106 within a predetermined distance from the humans 118, 406to perform a first command (e.g., stop performing physical activities).A second setting may cause MDUs 106 within a first distance from thehumans 118, 406 to perform a first command (e.g., stop performingphysical activities) and may cause MDUs 106 within a second distance toperform a second command (e.g., reduce speed when moving to a newlocation).

Thus, an area may include more than one zone and the behavior of MDUs ineach zone may be configurable depending on various factors. For example,the human may wear a locator device that has different settings thatdetermine the behavior of the MDUs when the human's presence (e.g., thelocator device's presence) is detected. In this way, humans can specifythe behavior of the MDUs in each zone. Other factors, such as time ofday, a particular zone that the human has entered, and the like may alsobe used by the safety management device 110 to determine the behavior ofthe MDUs. In this way, the MDUs may comply with safety regulations toprovide a functionally safe environment for humans.

Illustrative Architectures

FIG. 5 is an illustrative architecture 500 in which a message isdelivered to mobile drive units at a predetermined interval according tosome implementations. The architecture 500 may include mobile driveunits 106(1) through 106(N) (where N>1) that are communicatively coupledto the safety management device 110 via a network 105. The network 105may include one or more networks, including a wired network, a wirelessnetwork, or both. The network 105 may include technologies such asEthernet, Data Over Cable Service Interface Specification (DOCSIS),Fiber Optic cable, WiFi® (e.g., 802.11), Bluetooth®, Global System forMobile (GSM), Long Term Evolution (LTE), Universal Mobile TelephoneService (UMTS), Code Division Multiple Access (CDMA), another type ofnetwork technology, or any combination thereof.

Each mobile drive unit 106 may include one or more processors 502, oneor more memory devices (e.g., computer readable media 504), one or morebatteries (or other power sources) 506, a drive unit safety controller508, a transceiver 510, an MDU locator 512, one or more drivemechanisms, such as motors 514, or any combination thereof. The computerreadable media 504 may include non-transitory media to storeinstructions 516 that are executable by the processors 502 to performthe various functions of the MDU 106. The drive unit safety controller508 may govern the behavior of the MDU 106 to prevent the MDU 106 fromcausing injury to the human 118. The transceiver 510 may be capable oftransmitting and receiving messages using the network 105. The MDUlocator 512 may be used to transmit a location of each MDU 106(1)through 106(N) to the management devices 108, 110 using the transceiver510.

The operational and safety management devices 108, 110 may include oneor more processors 518, one or more memory devices, such as computerreadable media 520, a messaging controller 522, a main safety controller524, an input/output interface 526, an alarm system 528, a transceiver530, or any combination thereof. The computer readable media 520 mayinclude instructions 532 that are executable by the processors 518 toperform the various functions of the safety management device 110. Themessaging controller 522 may determine which particular messages are tobe sent to particular MDUs 106. The main safety controller 524 mayprovide various safety instructions including determining when toinstruct the MDU's 106 to stop performing any physical activity, when toreduce speed, when to navigate away from a human, etc. The input/outputinterface 526 may include various input and output devices, such as akeyboard a mouse, a trackball, a display device, other input/outputdevices, and the like. The alarm system 528 may cause an alarm to soundor be displayed in an area, such as the area 102, to alert human(s) thatare in the area to exit the area etc. The transceiver 530 may be used tosend messages to and receive messages from the MDUs 106.

The human 118 may be associated with (e.g., by wearing) the locatordevice 120. For example, the locator device 120 may be incorporated intoan identification badge, a hard hat, safety glasses, work boots,protective suit, or any other item that can be worn or carried by thehuman 118. The locator device 120 may include a transceiver 534 to sendmessages to or receive messages from the operational and safetymanagement devices 108, 110, the MDUs 106, or both. For example, thetransceiver 534 may send a message that includes location data 536 toenable the management devices 108, 110, the MDUs 106, or both todetermine a location of the human 118.

In some implementations, each of the MDUs 106 may send, at apredetermined interval (e.g., every M milliseconds, where M>0) a querymessage 538 (e.g., “continue operating?”) to the safety managementdevice 110. In response to receiving the query message 538, the safetymanagement device 110 may send a response message to individual ones ofthe MDUs 106. For example, when the safety management device 110determines that no human is present, the response message may be anactivity message 540 that instructs an MDU to continue performing a setof activities. When the safety management device 110 determines that ahuman is present, the response message may be a stop message 542 thatinstructs an MDU to temporarily (e.g., while the human 118 is present)stop performing any physical activities, or the response message may bea slow speed message 544 that instructs an MDU to temporarily (e.g.,while the human 118 is present) reduce a speed of the MDU whennavigating to a new location. Other response messages when a human ispresent are also possible, e.g., a response message that instructs anMDU to navigate away from the human 118, or combinations of the variousresponse messages when a human is present.

The query message 538 may include an identifier 546 that uniquelyidentifies each query message that the safety management device 110receives from each MDU. For example, the identifier 546 may include anidentity of the MDU 106 that is sending the query message 538 and atimestamp that includes a date and time that the query message 538 wascreated. If the query message 538 includes the identifier 546, theresponse message (e.g., one of the messages 540, 542, or 544) sent bythe safety management device 110 may include the identifier 546 toidentify the response message as corresponding to a particular querymessage. If a particular MDU of the MDUs 106 fails to receive a responsemessage that includes the identifier 546 of a most recently sent querymessage, the particular MDU may stop performing any physical activitiesuntil a response message including the identifier 546 is received,and/or one of the management devices 108, 110 instructs the particularMDU otherwise.

In other implementations, the MDUs 106 may not send the query message538. When no human is detected, the safety management device 110 mayperiodically broadcast (e.g., send) the activity message 540 to the MDUs106 to instruct each of the MDUs 106 to perform (or continue performing)a set of activities. In response to detecting the presence of the human118, the safety management device 110 may stop sending the activitymessage 540 to the MDUs 106 and/or instead periodically broadcast thestop message 542, the slow speed message 544 or other appropriatemessages when a human is present. After determining that the human 118has left the area in which the MDUs 106 were performing activities, thesafety management device 110 may resume broadcasting the activitymessage 540 to the MDUs 106 to instruct the MDUs 106 to resumeperforming the set of activities and/or perform a different set ofactivities.

As previously mentioned, if one of the MDUs 106, such as MDU 106(1),fails to receive the activity message 540, the MDU 106(1) may ceaseperforming any physical activity until the MDU 106(1) receives theactivity message 540. For example, in situations where the network 105malfunctions, the MDUs 106 move to a location where commands from theoperational management device 108 and/or the safety management device110 cannot be received, or other situations where the MDUs 106 do notreceive the activity message 540, the MDUs 106 may cease performing anyphysical activity until the activity message 540 is received, and/oruntil instructed otherwise. Thus, the activity message 540 may serve asa “heartbeat” such that if the MDUs 106 do not detect the heartbeat(e.g., receive the activity message 540), then the MDUs 106 may performa default action, such as ceasing to perform any physical activity. TheMDUs 106 may resume performing a set of actions when the MDUs 106 resumeperiodically receiving the activity message 540.

Thus, the MDUs 106 may perform a set of activities in an area (or zone)when they periodically receive the activity message 540 from the safetymanagement device 110 instructing them to perform the set of activities.If the safety management device 110 detects the human 118 in the area(or zone), the safety management device 110 may determine a distance ofeach of the MDUs 106 from the human 118 and send the stop message 542 orthe slow speed message 544 (or other messages) to each of the MDUs 106,e.g., based on the distance. The MDUs 106 may cease performing anyphysical activity if the MDUs 106 do not periodically receive theactivity message 540.

FIG. 6 is an illustrative architecture 600 that includes usingidentifiers (e.g., fiducial markers) to determine location informationaccording to some implementations. In some implementations, identifiers(e.g., fiducial markers), such as the identifiers 116 may be used todetermine a location of one or more of the MDUs 106, the human 118, orboth. For example, the identifiers 116(1) to 116(M) (where M>1) may beplaced at various locations in an area (e.g., the area 102 of FIGS.1-4). Each of the identifiers 116 may include corresponding locationdata 602(1) to 602(M). The identifiers 116 may comprise a physical code(e.g., a bar code, a quick response (QR) code, or other type ofscannable code) that can be read using an imaging device, such as anoptical scanner. Alternatively, the identifiers 116 may be broadcast(e.g., transmitted). For example, the identifiers 116 may include radiofrequency identifier (RFIDs), or the like that transmit informationstored thereon. In some cases, the identifiers 116 may include locationinformation, such as the location data 602, that identifies a locationcorresponding to each of the identifiers 116.

Each of the MDUs 106(1) through 106(N) may include an imaging device,such as a scanner 604, that is capable of scanning (e.g., reading) theidentifiers 602. Each time a particular one of the MDUs 106 passes by orover one of the identifiers 116, the scanner 604 may scan one of theidentifiers 602 and send MDU location data 606 to the management devices108, 110. For example, the MDU location data 606 may include a uniqueidentifier provided by each of the identifiers 602. The managementdevices 108, 110 may determine a location of each of the MDUs 106 afterreceiving the MDU location data 606. For example, MDU 106(1) may sendthe MDU location data 606 that includes the identifier 602(1) associatedwith the identifier 116(1). The management devices 108, 110 may receivethe MDU location data 606, determine that the identifier 602(1) isassociated with the identifier 116(1), and determine a location of theidentifier 116(1) to determine the location of the MDU 106(1).

Each human, such as the human 118, in an area (e.g., the area 102) maywear the locator device 120 that includes an imaging device, such as ascanner 608, that is capable of scanning (e.g., reading) the identifiers602. Each time the human 118 passes near one of the identifiers 116, thescanner 608 may scan one of the identifiers 602 and send the locationdata 536 to the management devices 108, 110. For example, the locationdata 536 may include a unique identifier provided by one of theidentifiers 602. The management device 108 may determine a location ofthe human 118 after receiving the location data 536. For example, thehuman 118 may send the location data 536 that includes the identifier602(1) associated with the identifier 116(1). The management devices108, 110 may receive the location data 536, determine that theidentifier 602(1) is associated with the identifier 116(1), anddetermine a location of the identifier 116(1) to determine the locationof the human 118.

The scanners 604, 608 (e.g., imaging devices) may be designed to scaneach of the identifiers 602 of the identifiers 116. For example, whenthe identifiers 602 are optically scannable or readable, the scanners604, 608 may be cameras or another type of imaging device. When theidentifiers 602 are RFID tags, the scanners 604, 608, may be RF scanners(e.g., RFID readers).

Thus, identifiers, such as fiducial markers, where each fiducial markerhas a unique corresponding identifier, may be used to determine alocation of the MDUs 106, the human 118, or both. The location data 536may enable the management devices 108, 110 to determine when the human118 is in or near an area 102 in which the MDUs 106 are performing a setof activities. In response to determining that the human 118 is in ornear the area 102, the management devices 108, 110 may send one or morecommands 610 instructing the MDUs 106 to temporarily cease performingthe set of activities. The one or more commands 610 may instruct theMDUs 106 to move to a new location, cease performing any activity,navigate away from the human, or any combination thereof. In response todetecting that the human 118 is no longer in or near the area (e.g., atleast a predetermined distance from the area), the management devices108, 110 may send additional commands instructing the MDUs 106 to resumeperforming the set of activities and/or perform a different set ofactivities.

In some situations, the management devices 108, 110 may send directions612 to the human 118. For example, the human 118 may be unfamiliar withthe layout of an area and the management devices 108, 110 may send thedirections 612 to enable the human 118 to reach a particular location(e.g., a safe zone), to avoid a zone in which MDUs are performingactivities, to exit an area to enable the MDUs to resume performingactivities, etc. The directions 612 may include text messages to bedisplayed on a mobile communication device or on the locator device 120associated with the human 118. The directions 612 may include multimedia(e.g., audio, video, or both) files to be played back on a mobilecommunication device or on the locator device 120 associated with thehuman 118.

FIG. 7 is an illustrative architecture 700 in which a mobile drive unitmay determine the presence of a human using presence data according tosome implementations. In some implementations, MDUs may be capable ofdetecting the presence of humans in addition to or instead of themanagement devices 108, 110. For example, the MDU 106(1) may detect thehuman 118 based on presence data 702 sent by the locator device 120 andreceived by the transceiver 510.

The locator device 120 may include one or more processors 704 (oranother type of logic execution mechanism) and one or more memorydevices, such as computer readable media 706, to store instructions 708that are executable by the one or more processors 704 (or logic) toperform the functions of the locator device 120. The locator device 120may periodically send (e.g., broadcast) the presence data 702.

In some cases, in response to detecting the presence data 702, one ormore of the MDUs 106 may notify the management device 108 that a humanis present while in other cases one of the MDUs 106 may notify otherMDUs 106 that a human is present. For example, the MDU 106(1) mayreceive the presence data 702 and determine that the human 118 is in ornear an area in which the MDUs 106 are performing a set of activities.In response, the MDU 106(1) may (i) send a message to the managementdevice 108 indicating that the human 118 is in or near the area, (ii)send a message to the other MDUs 106 (e.g., MDU 106(2) to MDU 106(N))indicating that the human 118 is in or near the area, or both. Inresponse to receiving the message from the MDU 106(1) indicating thatthe human 118 is in or near the area, the management device 108 may senda message to the other MDUs 106 (e.g., MDU 106(2) to MDU 106(N))indicating that the human 118 is in or near the area.

Thus, an MDU may detect the presence of a human using presence databroadcast by a locator device that is worn by the human. The MDU maynotify other MDUs of the presence of the human and/or the MDU may notifya management device and the management device may notify the other MDUsthat the human is present in the area. In response to being notified ofthe presence of the human in the area, the MDUs may temporarily ceaseperforming a set of activities, move to a new location, cease performingany activity, reduce speed, navigate away from the human, or anycombination thereof. The MDUs may resume performing the set ofactivities (or perform a different set of activities) after receiving amessage from a particular management device that the human is no longerin the area (e.g., the human is at least a predetermined distance fromthe area).

Example Processes

In the flow diagrams of FIGS. 8 and 9, each block represents one or moreoperations that can be implemented in hardware, software, or acombination thereof. In the context of software, the blocks representcomputer-executable instructions that, when executed by one or moreprocessors, cause the processors to perform the recited operations.Generally, computer-executable instructions include routines, programs,objects, modules, components, data structures, and the like that performparticular functions or implement particular abstract data types. Theorder in which the blocks are described is not intended to be construedas a limitation, and any number of the described operations can becombined in any order and/or in parallel to implement the processes. Fordiscussion purposes, the processes 800 and 900 are described withreference to the architectures 100, 200, 300, 400, 500, 600, and 700 asdescribed above, although other models, frameworks, systems andenvironments may implement these processes.

FIG. 8 is a flow diagram of an example process 800 that includes sendingan activity message according to some implementations. For example, theprocess 800 may be performed by the safety management device 110.

At 802, a query message may be received from individual mobile driveunits (of one or more mobile drive units) requesting permission tocontinue performing a set of activities in a physical area. For example,in FIG. 5, the safety management device 110 may periodically receive thequery message 538 from individual mobile drive units of the MDUs 106that are performing activities in an area (e.g., the area 102 of FIG.1).

At 804, one or more drive unit locations corresponding to one or moremobile drive units may be determined. For example, in FIG. 5, the safetymanagement device 110 may determine a location corresponding to each ofthe MDUs 106(1) to 106(N).

At 806, an activity message may be sent to the individual mobile driveunits instructing the individual mobile drive units to continueperforming the set of activities. For example, in FIG. 5, the safetymanagement device 110 may send an activity message 540 to each of theMDUs 106(1) to 106(N). The activity message 540 may include theidentifier 546 to indicate that the activity message 540 is being sentin response to receiving the query message 538.

At 808, if a human is detected at a first location within the physicalarea, a stop message is sent to at least a first mobile drive unit thatis within a first distance from the human. For example, in FIG. 1, thesafety management device 110 may determine that the MDU 106(1) is withinthe first distance 122 from the human 118 and send a stop message (e.g.,the stop message 542 of FIG. 5) instructing the MDU 106(1) to stopperforming any physical activities.

At 810, a slow speed message may be sent to at least a second mobiledrive unit that is within a second distance from the human. For example,in FIG. 1, the safety management device 110 may determine that the MDU106(2) is greater than the first distance 122 from the human 118 butwithin the second distance 124 from the human 118 and send a slow speedmessage (e.g., the slow speed message 544 of FIG. 5) instructing the MDU106(2) to reduce speed.

At 812, if the human moves to a second location within the physicalarea, a stop message is sent to at least a third mobile drive unit thatis within the first distance from the human. For example, in FIG. 2,when the human 118 moves to the second location 204, the safetymanagement device 110 may send a stop message (e.g., the stop message542 of FIG. 5) to the MDU 106(3) if the MDU 106(3) is within the firstdistance 122 from the human 118 at the second location 204.

At 814, if the human moves to a third location that is outside thephysical area, the activity message is sent to the one or more mobiledrive units. For example, in FIG. 1 or 2, when the safety managementdevice 110 determines that the human 118 has left the area 102, thesafety management device 110 may instruct the MDUs 106 to perform (orresume performing) a set of activities. To illustrate, the safetymanagement device 110 may send the activity message 540 to the MDUs 106.

FIG. 9 is a flow diagram of an example process 900 that includesinstructing mobile drive units to avoid a portion of an area accordingto some implementations. The process 900 may be performed by the safetymanagement device 110 of FIGS. 1-7.

At 902, a request may be received to create a fixed zone inside an areain which mobile drive units are performing a set of activities. Forexample, in FIG. 3, the safety management device 110 may receive arequest from the human 118 to create the fixed zone 302 in the area 102.

At 904, the mobile drive units may be instructed to place physicalbarriers around a perimeter of the fixed zone. For example, in FIG. 3,if the barriers 304 include physical barriers, the safety managementdevice 110 may instruct one or more of the MDUs 106 to place thephysical barriers around the perimeter of a portion of the area 102 thatincludes the fixed zone 302.

At 906, the mobile drive units may be instructed to place transmittersaround a perimeter of the fixed zone. For example, in FIG. 3, if thebarriers 304 include virtual barriers, the safety management device 110may instruct one or more of the MDUs 106 to place transmitters aroundthe perimeter of the fixed zone 302. The transmitters may transmit asignal to create a virtual barrier that causes the MDUs 106 to avoidentering the fixed zone 302.

At 908, the mobile drive units may be instructed to avoid entering aportion of the area that includes the fixed zone. For example, in FIG.3, to create a virtual barrier, the safety management device 110 mayinstruct one or more of the MDUs 106 to avoid entering the fixed zone302.

At 910, the mobile drive units may be instructed to remove the physicalbarriers from the perimeter of the fixed zone or remove or turn off thetransmitters if a human is no longer present in the fixed zone 302and/or the fixed 302 is no longer needed. For example, in FIG. 3, ifphysical barriers were placed around the perimeter of the fixed zone302, the safety management device 110 may instruct one or more of theMDUs 106 to remove the physical barriers from the perimeter of the fixedzone 302. If a virtual barrier was created using transmitters placedalong the perimeter of the fixed zone 302, the safety management device110 may instruct one or more of the MDUs 106 to remove or turn off thetransmitters to remove the virtual barrier.

At 912, the mobile drive units may be instructed to resume performingthe set of activities in the area. For example, in FIG. 3, when thesafety management device 110 determines that the human 118 is no longerwithin the area 102, the safety management device 110 may instruct theMDUs 106 to remove physical barriers, remove or turn off transmittersused to create a virtual barrier, or both. After removing any physicalbarriers and/or virtual barriers, the safety management device 110 mayinstruct the MDUs 106 to perform the set of activities, e.g., includingentering the fixed zone 302 to perform an activity from the set ofactivities.

CONCLUSION

Although the subject matter has been described in language specific tostructural features and/or methodological acts, it is to be understoodthat the subject matter defined in the appended claims is notnecessarily limited to the specific features or acts described. Rather,the specific features and acts are disclosed as illustrative forms ofimplementing the claims.

What is claimed is:
 1. A system comprising: one or more processors; oneor more non-transitory computer-readable storage media storinginstructions executable by the one or more processors to perform actscomprising: determining one or more drive unit locations correspondingto one or more mobile drive units; receiving a query message fromindividual mobile drive units of the one or more mobile drive units, thequery message requesting permission to perform a set of activities;transmitting an activity message to the one or more mobile drive unitsin response to the query message, the activity message instructingindividual mobile drive units of the one or more mobile drive units toperform the set of activities within a physical area; determining, via alocator device associated with a human, that a first location of thehuman is within the physical area; determining that a first mobile driveunit of the one or more mobile drive units is within a first distancefrom the first location of the human; and ceasing transmission of theactivity message to the first mobile drive unit, thereby causing thefirst mobile drive unit to stop performing the set of activities.
 2. Thesystem of claim 1, the acts further comprising: determining that asecond mobile drive unit is within a second distance from the firstlocation of the human; and transmitting a slow speed message instructingthe second mobile drive unit to reduce a speed at which the secondmobile drive unit is travelling within the physical area.
 3. The systemof claim 1, the acts further comprising: determining, via the locatordevice associated with the human, that the human has moved to a secondlocation within the physical area, determining that a third mobile driveunit of the one or more mobile drive units is within the first distancefrom the second location of the human; and ceasing transmission of theactivity message to the third mobile drive unit, thereby causing thethird mobile drive unit to stop performing the set of activities.
 4. Thesystem of claim 1, wherein the query message includes a uniqueidentifier associated with each mobile drive unit, and the activitymessage transmitted in response to the query message includes the uniqueidentifier.
 5. The system of claim 1, the acts further comprising:determining that the human has moved to a third location that is outsidethe physical area within which the one or more mobile drive units areperforming the set of activities; and resuming transmission of theactivity message instructing individual mobile drive units of the one ormore mobile drive units to perform the set of activities within thephysical area.
 6. A computer-implemented method, comprising: determininga drive unit location of a mobile drive unit that is performing a set ofactivities in a physical area; determining, via a locator deviceassociated with a human, a location of the human within the physicalarea; determining whether the drive unit location is less than apredetermined distance from the location of the human; and in responseto determining that the drive unit location is less than thepredetermined distance from the location of the human, ceasingtransmission of an activity message instructing the mobile drive unit toperform the set of activities, thereby causing the mobile drive unit tostop performing the set of activities.
 7. The method of claim 6, furthercomprising: in response to determining that the drive unit location isgreater than or equal to the predetermined distance from the location ofthe human, transmitting a message instructing the mobile drive unit toat least one of continue performing the set of activities, navigate awayfrom the location of the human, move to a new location, or reduce aspeed of the mobile drive unit.
 8. The method of claim 6, furthercomprising: in response to determining that the location of the human isoutside the physical area, resuming transmission of the activity messageinstructing the mobile drive unit to perform the set of activities. 9.The method of claim 8, wherein the activity message is transmitted at apredetermined time interval.
 10. The method of claim 6, furthercomprising: receiving a query message from the mobile drive unit that isperforming the set of activities in the physical area, the query messagerequesting permission for the mobile drive unit to perform the set ofactivities.
 11. The method of claim 10, wherein determining the driveunit location of the mobile drive unit is based at least partly on thequery message and comprises: retrieving a set of location coordinateswithin the physical area from the query message; and determining thedrive unit location based on the set of location coordinates.
 12. Themethod of claim 10, wherein determining the drive unit location of themobile drive unit is based at least partly on the query message andcomprises: determining the drive unit location based at least partly ona fiducial marker identifier included in the query message, the fiducialmarker identifier corresponding to a location of a fiducial marker readby an imaging device on the mobile drive unit.
 13. The method of claim6, further comprising: determining the location of the human based atleast partly on receiving, from the locator device associated with thehuman, location data that includes a fiducial marker identifierassociated with a fiducial marker read by the locator device.
 14. Themethod of claim 6, further comprising: determining the location of thehuman based at least partly on imaging data received from one or moreimaging devices located within the physical area, the one or moreimaging devices including at least one of a stationary camera fixed inthe physical area or a mobile camera mounted on the mobile drive unit,and the imaging data including data associated with at least one of thehuman or the locator device associated with the human.
 15. The method ofclaim 6, further comprising: determining the location of the human basedat least partly on sensor data provided by one or more sensors locatedwithin the physical area, the one or more sensors including at least oneof a heat sensor, an infrared sensor, a motion sensor, or a radiofrequency identifier (RFID) reader, and the sensor data including dataassociated with at least one of the human or the locator deviceassociated with the human.
 16. A system, comprising: a mobile driveunit; a locator device associated with a human; and a management deviceconfigured to perform acts comprising: initiating transmission of anactivity message instructing the mobile drive unit to perform a set ofactivities within a physical area; determining a drive unit location ofthe mobile drive unit; determining, via the locator device, a locationof the human within the physical area; and in response to determiningthat the drive unit location is less than a predetermined distance fromthe location of the human, ceasing the transmission of the activitymessage instructing the mobile drive unit to perform the set ofactivities, thereby causing the mobile drive unit to stop performing theset of activities.
 17. The system of claim 16, the acts furthercomprising: receiving, from the locator device, a fiducial markeridentifier associated with a fiducial marker from a plurality offiducial markers that are located within the physical area; anddetermining the location of the human based at least partly on thefiducial marker identifier.
 18. The system of claim 16, the acts furthercomprising: receiving sensor data from one or more sensors locatedwithin the physical area, the one or more sensors including at least oneof a heat sensor, an infrared sensor, a motion sensor, an opticalsensor, or a radio frequency identifier (RFID) reader; and determiningthe location of the human based at least partly on the sensor data, andthe sensor data including data associated with at least one of the humanor the locator device associated with the human.
 19. The system of claim16, the acts further comprising: sending an avoid instruction to themobile drive unit to avoid entering a portion of the physical area, theavoid instruction including a set of spatial coordinates associated withthe portion of the physical area; monitoring the location of the human;modifying the set of spatial coordinates included in the avoidinstruction based at least partly on the location of the human to createmodified spatial coordinates; and sending the avoid instructionincluding the modified spatial coordinates to the mobile drive unit. 20.The system of claim 16, the acts further comprising: sending a zoneinstruction to the mobile drive unit to place a plurality of objectsalong a perimeter of a portion of the physical area to create a safezone at least partially surrounding the location of the human, theplurality of objects including at least one of a transmitter, a lightcurtain, or a physical barrier.